Characterization of Biochar from Beach-Cast Seaweed and Its Use for Amelioration of Acid Soils

Limited knowledge is available regarding biochar (BC) obtained from beach-cast seaweed, which needs to be characterized to better prospect its potential applications. Beach-cast seaweed BCs were produced at two temperatures (300 and 600 °C) and two residence times (1 and 3 h). First, an extensive characterization of feedstock and their derived BCs was performed. Then, an incubation experiment was conducted to investigate the potential of these BCs as ameliorants in two acidic soils, classified as Umbrisols. Proximate and elemental analyses suggested the presence of more stable C structures in BCs at 600 °C with a high C, fixed carbon (FC) and low H, O and volatile matter (VM); additionally, thermogravimetric graphics showed less weight loss. Some features from the raw material were present in biochars obtained at 300 °C but absent at 600 °C. Dissolved organic carbon was much lower in BCs pyrolyzed at 600 °C than at 300 °C, suggesting the higher aromaticity of the former, allowing more resistance to water extraction. The breakdown of proteinaceous soluble materials after pyrolysis was revealed by fluorescence. Residence time caused minor effects in biochar properties compared to temperature. The soil pH and macronutrient availability of the two studied soils increased after beach-cast seaweed biochar addition.